A rotorcraft is an aircraft that obtains lift from rotating rotor blades instead of a fixed wing. The blades are carried in a rotor head which allows them to spin. An autogiro has no engine power to the blades, it's blades being powered by the wind as the aircraft moves forward. It usually uses a teetering rotor head, because they are easy to build and maintain. A helicopter, by contrast, is a rotorcraft with engine power to the blades, that can change the pitch of the blades allowing it to hover and take off vertically. This is a great additional ability, but it comes at a great price. Helicopters are very complicated and expensive both to manufacture and to maintain. They also require a great deal more training and skill to fly.
This invention describes a pitch changing teetering rotor head designed primarily for the single and two-place autogiro, but adaptable for all teetering head rotorcraft of any size or configuration including but not limited to autogiros, helicopters, drones, and radio-controlled toys. These documents constitute the best mode for creating and using this invention.
Spinning rotor blades require many things to happen at one time and on different axes with different motions, rotor blade spin on a vertical axis, teetering on a horizontal axis, with horizontal flap and vertical lead and lag mostly accommodated by the teetering motion, the addition of a feathering axis to twist the blades to change the pitch has necessitated a very complicated rotor head to accomplish all of this at once.
This complication and expense has put the vital capability of rotor blade pitch change, and the concomitant ability to take off vertically, out of the reach of the small autogiro community, and has made helicopters the only and very expensive option.
Prior inventors developed the teetering rotor head initially for autogiros, which resolves the spin and flap forces with a very elegant simplicity, but until now no one has succeeded in adding pitch change without also adding too much of the complexity of the helicopter rotor head.
The lack of pitch change in the commonly used teetering rotor head means that the autogiro requires a runway to become airborne, which severely limits its flexibility. It can land in a very small space or rough field, but cannot take off again from that space or rough field.
At the present time rotor blade pre-rotators can only be used to provide an RPM less than flying speed, since flying speed will break contact with the ground, and the torque from the pre-rotator motor will cause the fuselage to spin, a loss of control, and a serious crash. Thus they can shorten the runway needed but not eliminate it.
In using the pitch change capability of this rotor head for vertical take off, the pitch of the blades is reduced to reduce lift and drag, and a pre-rotator device is used to spin up the blades to more than flying speed. More than flying speed becomes safe because reducing pitch reduces lift so that contact with the ground is not lost. The pre-rotator is then disengaged, eliminating the torque that would spin the fuselage, and the pitch is increased to a flying angle. With the power of the stored kinetic energy in the free-spinning blades, the autogiro will literally leap straight up into the air, and forward propulsion is applied to maintain flight. No runway needed.
The key is that to be successful, it must be financially viable as well as mechanically viable. Previous designs may have been mechanically viable, but still too complicated and expensive to be practical, so not financially viable.
A large proportion of the one and two place autogiro community consists of home-builders and tinkerers who need to fly on the cheap, which usually means make it yourself in your garage. This pitch change rotorhead can be made with ordinary shop tools, a drill press, table or radial arm saw, and lathe, and with ordinarily obtainable materials, no special castings required. For a homebuilder, the cost to make it is only slightly more than a standard teetering rotor head, yet the gain in usefulness and flexibility is monumental. This invention is needed precisely because it is the affordable alternative.